(1) Field of the Invention
The invention relates to a method for production of a plastic injection-moulded part having a component made of ceramic or glass embedded in it, which plastic injection-moulded part can be a shell body of a rapid diagnosis appliance.
(2) Description of Related Art
In rapid diagnosis appliances, such as those used for determining blood sugar levels or for determining other blood values, it is often necessary to heat the reagent area inside the appliance housing of the rapid diagnosis appliance. Test strips wetted with human or animal blood, for example, are inserted into the evaluation area of a rapid diagnosis appliance. It is also possible to first introduce the test strip into the rapid diagnosis appliance and only thereafter apply the sample to the test strip. The test strips contain substances which react with the area of the test strip wetted with the blood of human or animal origin. To perform a measurement procedure yielding a meaningful measurement result, a defined temperature is needed during the evaluation procedure.
To generate an appropriate temperature level, metal or ceramic heating elements are therefore integrated in the interior of the housing body of the rapid diagnosis appliance. These heating elements are normally embedded in plastic components in the critical system environment. The heating elements made of metal or ceramic materials are generally embedded by mechanical securing with springs or clip elements, or by adhesively bonding the heating element made of metal or ceramic into a depression provided for this purpose in the plastic material.
The disadvantages of mechanically securing the ceramic or metal heating element inside a plastic component are that the spring elements or clip elements exerting spring forces on the heating element can induce stresses in a heating element made of ceramic for example, which can lead to its fracturing, with the result that the heating element integrated for example in the rapid diagnosis appliance is rendered unusable. Moreover, when the heating element is mounted mechanically in the inside of the housing, the resulting seams, caused by production tolerances, may mean that if too much blood is applied to the test strip, blood can pass through the seams into the inside of the appliance and cause damage there to the evaluation electronics. The same applies to a cleaning agent with which the inside of the appliance is cleaned after several test strip evaluations in order to remove dried blood plasma which, for example, has accumulated on the heating element made of metal or ceramic. The cleaning agents used are often very aggressive so as to be able to dissolve and remove the blood plasma which has accumulated mainly on the surface of the metal or ceramic heating element. If the cleaning agent, which often has an extreme dissolving action, passes into the inside of the appliance through the seams which arise in mechanical mounting of the metal or ceramic heating element, then the electronics may also be damaged by the cleaning agent.
The option of mechanically securing a ceramic or metal heating element inside a rapid diagnosis appliance additionally has the disadvantage of high costs of assembly, and the risk of incorrect assembly is not inconsiderable. If a heating element to be introduced at a later stage into a plastic component is incorrectly assembled, this can result in temperature control errors which may have the effect that the measurement results obtained from an evaluation of a test strip inserted into the rapid diagnosis appliance are often rendered unusable.
Instead of the mechanical securing option, the heating element made of metal or ceramic material can also be adhesively bonded into a corresponding depression of a half shell in the inside of the rapid diagnosis appliance. By adhesively bonding a metal or ceramic heating element into a recess in the inside of the rapid diagnosis appliance, it is possible to largely avoid the seams which arise in the securing option discussed above, but the solvents admixed to the adhesive can affect the test strip inserted into the inside of the appliance. Moreover, it is not possible to avoid a situation where the cleaning agents, with which the heating element is cleaned in order to remove dried blood plasma from time to time, dissolve the adhesive with which the heating element is bonded into a depression inside the housing interior. Moreover, all adhesives are subject to aging during the period of operation, particularly in the event of large temperature fluctuations, which means that this securing option is associated with risks concerning the reliability of a rapid diagnosis appliance over the period of its use.
Moreover, in this type of securing, the high cost of assembly is a disadvantage if this option is used in large-scale production, for example as in the large-scale production of rapid diagnosis appliances. Here too, the production process is not free from assembly errors which, in accordance with what has been stated above, can considerably compromise the meaningfulness of the evaluation result obtained.
A further option for securing a component, for example a heating element made of metal or ceramic material, inside a plastic injection-moulded part is to inject it directly as an insert in the injection-moulding of the plastic injection-moulded part. The problem with this method of production is that the pressure arising inside the injection mould is problematic for breakable materials, for example ceramics, since breakable materials like ceramic or glass cannot be randomly pressed.